Charging, accounting and billing are crucial features of communication systems and services. The network provider must design tariffs for the whole range of services offered. This is partly a marketing decision, tariffs should be attractive to customers, but network providers are also concerned with technical efficiency and cost-recovery. Charging schemes should encourage the customers for efficient use of the network resources and should generate revenue in a fair way according to the relative usage by the customers. The development of multiservice and multilayer next generation mobile networks (NGMN) poses new challenges to the design of charging schemes. In multiservice networks, tariffs can depend on a number of parameters which define the traffic and quality of service (QoS) characteristics of a connection. Charges should reflect network resource usage. The way a customer uses the network depends on the tariffs and how the customer values each type of connection. Charging periods have been used in the field of telecommunications networks to provide differentiated pricing per charging period, such as so called time of day accounting. With the advent of next generation networks such as 5G, for example, new network functions, layers, infrastructures and services can be realized. The current charging schemes are no longer suitable to guarantee a fair charging of used network resources and to avoid inefficient usage of network resources.